Speak, under pressure, in golf club (6)
I believe the answer is:
putter
'golf club' is the definition.
(I've seen this before)
'speak under pressure' is the wordplay.
'speak' becomes 'utter' (synonyms).
'under' says to put letters next to each other.
'pressure' becomes 'p' (abbreviation).
'utter' after 'p' is 'PUTTER'.
'in' is the link.
(Other definitions for putter that I've seen before include "Club used on the green" , "Golf-club" , "Golf club used on greens" , "Type of golf club" , "Club to use on the green" .)